DC-DC power management refers to DC to DC power supply (directcurrent). The utility model relates to a device for converting electric energy of one voltage value into electric energy of another voltage value in a DC circuit.
For example, a DC voltage (5.0V) can be converted into other DC voltages (1.5V or 12.0V) through a converter. We call this converter DC-DC power management, or switching power supply or switching regulator.
DC-DC power management is generally composed of control chip, inductor coil, diode, triode and capacitor.
When discussing the performance of DC-DC power management, if it is only for the control chip, it can not judge its advantages and disadvantages. The component characteristics of the peripheral circuit and the wiring mode of the substrate can change the performance of the power circuit. Therefore, comprehensive judgment should be made.
The use of DC-DC power management is conducive to simplify the power circuit design, shorten the development cycle and achieve the best indicators. It is widely used in power electronics, military industry, scientific research, industrial control equipment, communication equipment, instruments, switching equipment, access equipment, mobile communication, router and other communication fields, as well as industrial control, automotive electronics, aerospace and other fields.
With the characteristics of high reliability and easy system upgrade, the application of power module is more and more widely. In addition, DC-DC power management is also widely used in mobile phones, MP3, digital cameras, portable media players and other products. It belongs to chopper circuit in circuit type classification.
Its main feature is high efficiency: compared with LDO of linear regulator, high efficiency is a significant advantage of DC-DC. Generally, the efficiency is more than 70%, and the high efficiency can reach more than 95%. The second is to adapt to a wide voltage range.
DC-DC has three common principle architectures:
1. Buck (Buck DC / DC converter)
2. Boost (boost DC / DC converter)
3. Buck boost (buck boost DC / DC converter)
Design skills and selection requirements of main technical parameters
At least the following conditions shall be considered in the design of DC-DC circuit:
The range of external input power supply voltage and the size of output current.
Maximum value of DC-DC output voltage, current and system power.
1. Input / output voltage
It shall be selected according to the recommended working voltage range of the device, and the fluctuation range of the actual voltage shall be considered to ensure that the device specification cannot be exceeded.
2. Output current
The continuous output current capability of the device is an important parameter, which should be referred to when selecting, and a certain margin should be reserved.
The selection of this parameter also needs to evaluate the instantaneous peak current and heating of the circuit, determine it comprehensively, and meet the derating requirements.
3. Ripple
Ripple is an important parameter to measure the output voltage fluctuation of the circuit. Pay attention to light load and heavy load ripple. Generally, light load ripple should be large. Pay attention to whether the light load ripple will exceed the requirements in nuclear power and other occasions. Actual test under various scenario loads. Generally, 20m bandwidth of oscilloscope is selected for test.
4. Efficiency
Pay attention to both light load and heavy load. Light load will affect standby power and heavy load will affect temperature rise. Generally speaking, the efficiency of 10mA under 12V input and 5V output is generally more than 80%.
5. Transient response
Transient response characteristics reflect whether the system can be adjusted in time to ensure the stability of output voltage when the load changes sharply. It is required that the smaller the output voltage fluctuation, the better. Generally, it is required that the peak value is less than 10%.
In practice, pay attention to the selection of feedback capacitor according to the recommended value. Common values range from 22P to 120pf.
6. Switching frequency
Most of the commonly used switching frequencies are above 500KHz. There are also high switching frequencies of 1.2m to 2m. Due to the high frequency, the switching loss increases and the IC heat dissipation design is better, so it is mainly concentrated in the products with 5V low-voltage input and small current. Switching frequency is related to the selection of inductance and capacitance, and other problems such as EMC and noise under light load are also related to it.
7. Feedback reference voltage and accuracy
The feedback voltage shall be compared with the internal reference voltage, and different voltages shall be output in cooperation with the external feedback voltage dividing resistance. The reference voltage of different products will be different, such as 0.6 ~ 0.8V. Pay attention to adjusting the feedback resistance during replacement.
The feedback resistance shall be selected with 1% accuracy. As long as it is selected according to the manufacturer's recommendation, it is generally not too large to avoid affecting the stability.
The accuracy of reference voltage affects the output accuracy. The common accuracy is less than 2%, such as 1% ~ 1.5%. The cost of products with high accuracy will be different. Select as needed.
8. Linear stability and load stability
Linear stability reflects the change of input voltage and the stability of output voltage. The load stability reflects the output voltage stability when the output load changes. The general requirement is 1%, and the maximum is not more than 3%.
9. En level
EN high and low levels shall meet the requirements of device specifications, and some ICs shall not exceed the specific voltage range; When dividing the resistance voltage, pay attention to timely turn off, and consider the maximum range of voltage fluctuation.
Due to the need of timing control, the pin will increase the capacitance. In order to adjust the level and turn off the discharge, there should be a resistance to ground at the same time.
10. Protection performance
There shall be overcurrent protection OCP, overheating protection OTP, etc., and the conditions can recover after the protection disappears.
11. Others
Soft start is required; Thermal resistance and packaging; The use temperature range shall be able to cover high and low temperature, etc.
General principles of device selection
universality
High cost performance
Easy procurement and long life cycle
Compatible and replaceable
Resource conservation
Derating
Easy production and normalization
DC-DC power management chip is highly integrated and powerful. Its complex internal structure has brought great difficulties to her performance and parameter test. What are the difficulties in the test of AC-DC chip? Let's follow Li Microelectronics:
First, the internal structure of DC-DC power management chip is complex. To test it, we need to have a deep understanding and understanding of the working principle of the circuit, the structural composition of the circuit and the relationship between the components, the principle of test parameters and corresponding test methods.
Second, the AC-DC chip contains many relatively independent parts. In order to test the relevant parameters of each part, it is necessary to design a special test circuit to cover all test items, so the test system needs to have corresponding supporting facilities, such as the measurement route (TMU) of test time parameters, the precision unit (PMU) of test output characteristics, etc, Moreover, the parameters required by the AC-DC chip include different types of physical quantities, such as frequency, time, voltage, current, etc. in addition, they also include some threshold values that need to be scanned and tested. Therefore, the retest system must have a special test route for different parts and different physical quantities.
Thirdly, because the internal modules of DC-DC power management switching power supply chip interact with each other, when a parameter is tested, the influence of other modules needs to be considered, that is, the working mode of the whole device and the relationship of each sub module under the working mode need to be considered.
Fourth, because some parameters of AC-DC chip are sensitive to test, it is required that the distance between the test route and the periphery of the circuit under test should not be too large, or during the test, some small states of some pins will affect the test accuracy of the parameters, and even cause the function to disappear, Therefore, when designing the test scheme, we need to consider how to deal with some peripheral routes controlled as.